Diversity in tropical forest edges....

Interesting things happen at the edges, whether of continental plates or cultural periods. In ecology, too, the edges of habitats--called ecotones--are happening places. If they're large enough, they can be cradles of biological diversity, researchers report in the June 20 Science.

Biologist Thomas B. Smith of San Francisco State University and his colleagues studied a dozen populations of a small bird, the little greenbul (Andropadus virens), in Cameroon. Half of the populations lived in the dense tropical rain forest, while the other half came from the extensive and patchy edge habitat that separates the forest from the savanna. Although all of the birds were genetically similar and could interbreed, those from the edge habitat differed physically from the forest birds. They weighed more and had longer wings, for example.

The researchers maintain that these differences--as significant as the differences between some species--are good evidence of natural selection linked to the habitats the bird populations occupy. Longer wings might offer a faster means of escape in the edge habitat, where predators may be a greater problem. These habitats, though relatively neglected by conservationists, may therefore "be integral to the production and maintenance of biodiversity in tropical rain forests," the researchers say.